Hydride sponge

Hydride sponge. This compound abstracts hydride from triorganoborohy-drides and Cp2ZrClH.1 It also forms an adduct with F but interacts only weakly with Cl" and Br. ... 

Hydride Sponge and Other Lewis Acid Chelates... 

Figure 4.30 (a) Comparison of proton sponge and hydride sponge , (b) X-ray crystal of the anion... 

Lewis acids based on boronic acid derivatives or main group elements such as mercury, tin and silicon form strong bonds to anions with considerable covalency, exemplified by hydride sponge and the anticrowns. 

Suggest experimental techniques for assessing the affinity of a host for a particular anion in solution. Which of these techniques might be appropriate for (a) podand (4.40), (b) diboryl hosts such as hydride sponge (4.69) and (c) zwitterions such as (4.35). 

Katz, H. E., Hydride Sponge Complexation of l,8-naphthalenediylbis(dimethylborane) with hydride, fluoride and hydroxide. J. Org. Chem 1985, 50, 5027-5032. 

The starting point for the synthesis of /ten-borylated naphthalenes is 1,8-dilithionaphthalene, which may also be transformed into other useful reagents such as 1,8-distannylated and 1,8-dunercuriated naphthalenes. Since the initial report of Katz on the unusual properties of 1,8-bis(dimethylboryl)naphthalene (51) as a hydride-sponge new... 

Katz (79, 80) used 23 as a receptor for anions, studying its interaction with hydride, fluoride, and hydroxide ions. Comparison with 24 once again indicated a chelate effect compound 23 abstracting hydride or fluoride from complexed 24. The crystal structure of the hydride sponge 23, showed the hydride ion bound between the pair of boron atoms with short strong bonds. A crystal structure of the chloride complex was also elucidated and showed the same bridged structure (81). 

An intriguing question is whether the use of bidentate Lewis acids may be advantageous for the selective recognition of anions. Early studies by Shriver, Katz, Koester, and Wrackmeyer show that a bidentate organoboron Lewis acid may coordinate a nucleophile in a bridging fashion as illustrated for Katz s hydride-sponge in Scheme 24. The relatively short distance of ca. 3 A between the boron centers of 1,8-diborylated naphthalenes allows for effective coordination of nucleophiles in a reverse chelate fashion. Many other... 

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